CN117525418A

CN117525418A - Electrode for secondary battery having improved rapid charge performance, method of manufacturing the same, and secondary battery including the same

Info

Publication number: CN117525418A
Application number: CN202311595948.1A
Authority: CN
Inventors: 李东勋; 金在渊; 梁眐珉
Original assignee: SK On Co Ltd
Current assignee: SK On Co Ltd
Priority date: 2020-09-28
Filing date: 2021-09-26
Publication date: 2024-02-06
Also published as: JP2022055354A; KR20230022915A; CN114335413B; US20240120485A1; CN114335413A; US20220102727A1; US20240154122A1; EP3975284A1

Abstract

The present invention relates to an electrode for a secondary battery, a method of manufacturing the electrode, and a secondary battery including the electrode, the electrode being characterized by comprising: a current collector; and an electrode active material layer that is positioned on at least one surface of the current collector and satisfies relation 1.

Description

Electrode for secondary battery having improved rapid charge performance, method of manufacturing the same, and secondary battery including the same

The present application is a divisional application of chinese patent application having a filing date of 2021, 9 and 26, a chinese patent application number of 202111126298.7 and a name of "electrode for secondary battery with improved rapid charging performance, method of manufacturing the same, and secondary battery including the same", and claims to enjoy priority of KR 10-2020-0125242 and KR 10-2021-0028808.

Technical Field

The present invention relates to an electrode for a secondary battery having improved rapid charging performance, a method of manufacturing the electrode, and a secondary battery including the electrode.

Background

In recent years, in a large-sized battery (Cell) for high-energy EV, since the density of an electrode is high, when the battery is charged at a high current density, diffusion (diffusion) of Li ions into the inside of a negative electrode is limited, and in this case, li ions are deposited on the surface of the negative electrode, resulting in degradation of the battery.

In order to improve the above-described problems, it is important to keep the density of the anode as low as possible, or to reduce the resistance of the anode surface and inside so that Li ions can rapidly diffuse into the anode inside.

In order to improve the resistance and the quick charge performance of the battery, an adhesive having high adhesion is developed, and a technology for reducing the content of the adhesive using the adhesive is being developed, but the kind of the adhesive having high adhesion and the reduction of the content of the adhesive are limited, and when the content of the adhesive is too low, a serious problem occurs in that the electrode mixture layer is detached from the current collector during a cutting (Notching) process or the charge and discharge of the battery.

Accordingly, a technology for effectively distributing a binder inside a negative electrode has been developed, in which the binder content of a negative electrode mixture layer and the surface can be reduced while suppressing detachment by forming a high content of binder at the interface of a current collector, and thus battery performance can be improved. For this reason, a technology of forming a negative electrode slurry (slurry) having a high binder content in a lower layer mainly in the form of a double layer (Dual layer) and preparing a negative electrode slurry having a low binder content in an upper layer has been developed, but in a general drying process, there is a limitation in achieving a desired binder distribution due to a phenomenon in which binder particles move to the surface of a negative electrode mixture layer.

In order to improve the adhesion between the current collector and the surface of the negative electrode and to maintain electrical contact as much as possible, a technique has been developed in which a substrate coated with a conductive agent such as Carbon black (Carbon black) or Carbon Nanotube (CNT) is prepared on the current collector and a negative electrode mixture layer is formed on the upper portion of the current collector, but the effect of improving the battery performance is insufficient.

Therefore, there is a need to develop a secondary battery having a low interfacial resistivity value between current collector-electrode mixture layers and improved rapid charging performance.

Disclosure of Invention

Technical problem to be solved

The purpose of the electrode for a secondary battery is to improve the interfacial adhesion between a current collector and an electrode active material layer, and to improve the quick charge performance while preventing process defects such as detachment of the electrode and appearance defects.

The method for manufacturing an electrode for a secondary battery of the present invention is directed to manufacturing an electrode that has improved interfacial adhesion and prevents process defects and appearance defects while allowing rapid charging.

Technical proposal

One embodiment of the present invention provides an electrode for a secondary battery, including: a current collector; and an electrode active material layer that is positioned on at least one surface of the current collector and satisfies the following relation 1.

[ relation 1]

t ₂ ≤t ₁ ≤8×t ₂

In the relation 1, t ₁ Is based on the position where separation occurs inside the electrode active material layer when measuring the 90 DEG bending adhesive force of the electrode, and is close to the collectorThickness of electrode active material layer other than current collector on fluid side, t ₂ Is the particle size (D50) of the electrode active material contained in the electrode active material layer.

The electrode may also satisfy the following relation 2.

[ relation 2]

1.5×t ₂ ≤t ₁ ≤5×t ₂

In the relation 2, t ₁ Is the thickness of the electrode active material layer, t, on the side of the current collector, excluding the current collector, based on the position where separation occurs inside the electrode active material layer when measuring the 90 DEG bending adhesion of the electrode ₂ Is the particle size (D50) of the electrode active material contained in the electrode active material layer.

The electrode active material layer may include a styrene-butadiene rubber (Styrene butadiene rubber, SBR) -based binder.

The electrode active material layer may contain 0.1 to 2 wt% of the binder with respect to the total weight.

The electrode may also satisfy the following relation 3.

[ relation 3]

0.25≤b ₂ /b ₁ <0.7

In the relation 3, b when the binder distribution is measured in the thickness direction of the electrode active material layer ₁ Is the weight of the binder in the whole electrode active material layer, b ₂ Is the weight of the binder in the region of 15% of the total thickness from the current collector to the electrode active material layer.

The electrode may also satisfy the following relation 4.

[ relation 4]

0.3≤b ₂ /b ₁ <0.5

In the relation 4, b when the binder distribution is measured in the thickness direction of the electrode active material layer ₁ Is the weight of the binder in the whole electrode active material layer, b ₂ Is in the region of 15% of the total thickness from the current collector to the electrode active material layerIs added to the adhesive.

The electrode may have a continuous binder concentration in the thickness direction of the electrode.

The electrode may also satisfy the following relation 5.

[ relation 5]

-30％≤(C-D)/D≤+30％

In the relation 5, C is an interfacial adhesion force between the current collector and the electrode active material layer measured at an arbitrary position selected in the width direction of the electrode active material layer, and D is an average value of interfacial adhesion forces between the current collector and the electrode active material layer.

The electrode may be a negative electrode.

Another embodiment of the present invention provides a method of manufacturing an electrode for a secondary battery, the method including the steps of: a) Coating an adhesive suspension on at least one side of a current collector; b) Coating an electrode slurry containing an electrode active material on an upper portion of the binder suspension; and c) drying the product of step b), wherein steps a) and b) are performed simultaneously or sequentially.

In the step a), the adhesive suspension may be uniformly coated on one side of the current collector.

In the step a), the adhesive suspension may have a coating thickness of 0.1 to 10 μm.

The binder suspension may contain 30 wt% or more of the binder with respect to the total amount of solids, and the electrode slurry may contain 2 wt% or less of the binder with respect to the total amount of solids.

The step c) may be carried out at a temperature of 50-200 ℃ for 30-300 seconds.

Another embodiment provides an electrode for a secondary battery, which is an electrode for a secondary battery manufactured by: a) Coating an adhesive suspension on at least one side of a current collector; b) Coating an electrode slurry containing an electrode active material on an upper portion of the binder suspension; and c) drying the product of step b), wherein steps a) and b) are performed simultaneously or sequentially.

Another embodiment provides a secondary battery including: the electrode; a diaphragm; and (3) an electrolyte.

Advantageous effects

The invention can improve the interfacial adhesion between the current collector and the electrode active material layer, improve the poor process such as electrode detachment and the like, and improve the quick charge performance.

Drawings

Fig. 1 and 2 are SEM images showing cross sections in the thickness direction of the negative electrodes manufactured in example 1 and comparative example 6.

Fig. 3 and 4 are diagrams showing EDS mapping (mapping) results in the thickness direction of the negative electrode manufactured in example 1.

Fig. 5 is a schematic view showing a state in which 90 ° bending adhesion was measured for the negative electrodes manufactured in examples 1 to 4 and comparative examples 1 to 6 and the current collector and the negative electrode active material layer were separated.

Fig. 6a and 6b are diagrams showing photographs of an evaluation method of interfacial adhesion (90 ° bending adhesion) of an electrode active material layer and a current collector.

Fig. 6c is a view showing a photograph of the separated negative electrode after 90 ° bending adhesion measurement of the negative electrodes of example 1 and comparative example 1.

Fig. 7 and 8 are graphs showing interfacial adhesion force between a current collector and a negative electrode active material layer measured at a position in the width direction of the negative electrode active material layer and dispersion (%) of the adhesion force.

Description of the reference numerals

1: current collector

3: adhesive layer

5: electrode active material layer

11: adhesive agent

Detailed Description

The advantages and features of the present invention and the method of accomplishing the same may be understood clearly by reference to the accompanying drawings and the detailed description of embodiments. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various ways different from each other, which are provided for completely disclosing the present invention and completely explaining the scope of the invention to those skilled in the art, and the present invention is limited only by the scope of the claims. Specific details for carrying out the invention are set forth in detail with reference to the accompanying drawings. Irrespective of the figures, like reference numerals refer to like constituent elements, "and/or" includes all combinations of the individual items mentioned and more than one of the items mentioned.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Throughout this specification, unless the contrary is intended to cover a particular feature, the description "comprising" or "comprises" of a feature means that other features may also be included, rather than excluding other features. Furthermore, the singular forms also include the plural unless specifically stated otherwise.

In this specification, when a portion of a layer, a film, a region, a plate, or the like is described as being "on" or "upper" of another portion, this includes not only the case of being "directly over" the other portion but also the case of having the other portion in the middle thereof.

One embodiment of the present invention provides an electrode for a secondary battery. The electrode for a secondary battery includes: a current collector; and an electrode active material layer that is positioned on at least one surface of the current collector and satisfies the following relation 1. The secondary battery may be a lithium secondary battery.

[ relation 1]

t ₂ ≤t ₁ ≤8×t ₂

In the relation 1, t ₁ Is the thickness of the electrode active material layer, t, on the side of the current collector, excluding the current collector, based on the position where separation occurs inside the electrode active material layer when measuring the 90 DEG bending adhesion of the electrode ₂ Is the particle size (D50) of the electrode active material contained in the electrode active material layer.

The electrode active material layer may be formed by applying a binder suspension to at least one side of the current collector and applying an electrode slurry on the applied binder suspension, or drying a product in which the binder suspension and the electrode slurry are simultaneously applied to at least one side of the current collector.

The adhesive suspension may be prepared to contain an adhesive and a solvent. The suspension (suspension) refers to a mixture in which the binder is not dissolved but exists in the form of particles in a solvent, and if necessary, a thickener, a conductive material, and the like may be further mixed and used.

The adhesive may include a Styrene-butadiene rubber-based adhesive, for example, styrene-butadiene rubber, styrene-butadiene acrylate copolymer (Styrene-butadiene acrylate copolymer), etc., but the present invention is not limited thereto. Accordingly, the electrode active material layer may include a Styrene Butadiene Rubber (SBR) -based binder.

The electrode active material layer may contain 0.1 to 2 wt% or 0.1 to 1.8 wt% or 0.5 to 1.5 wt% of the binder with respect to the total weight. In the present invention, by distributing a large amount of binder at the interface of the current collector and the active material layer and reducing the binder content on the electrode surface side, the total amount of binder contained in the entire active material layer can be significantly reduced. Thus, the interfacial adhesion between the current collector and the active material layer can be improved while also improving the rapid charging performance.

When the SBR-based binder or the like is used, since the binder is mixed in the form of particles, the viscosity of the binder suspension is very low. Further, since the binder particle size is formed in a small size of 200nm or less, when the upper electrode slurry is applied and dried, the binder particles are easily diffused into the upper electrode active material layer due to osmotic pressure, and there is a possibility that a significant binder layer is not formed between the current collector and the active material layer after drying. Further, since the SBR-based binder is excellent in spreadability with the current collector, it may be uniformly coated in a width direction of the current collector with a relatively thin thickness without forming a separate pattern, and thus the adhesive force between the current collector and the electrode active material layer may be uniformly improved. On the other hand, polyacrylic acid (PAA), polyvinylidene fluoride (PVdF), and the like, which can be used as an electrode binder, are applied in a state of being dissolved in a solvent, unlike the SBR-based binder and the like, and the solvent is sufficiently dried when the electrode is dried, and then phase-separated to form a binder layer. Therefore, the binder is difficult to diffuse (migrate) to the upper electrode active material layer during the drying process, and thus a significant binder layer may be formed between the current collector and the active material layer. Further, it is not possible to uniformly distribute in the current collector width direction and form patterns (e.g., island type, dot type), and thus the adhesive force and interfacial resistivity value between the current collector and the active material layer are not excellent.

The solvent may be at least one selected from the group consisting of water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propyl alcohol, and t-butyl alcohol, but is not limited thereto.

The adhesive suspension may also contain a thickener for imparting tackiness to produce a stable solution. As an example, a cellulose compound may be used as the thickener, and specifically, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, alkali metal salts thereof, and the like may be mixed and used. The alkali metal may be Na, K or Li.

The conductive material is used for imparting conductivity to the electrode, and is not particularly limited as long as it is a conventional conductive material that does not cause chemical changes in the battery. As an example, the conductive material may use a material selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, and combinations thereof, but is not limited thereto.

The current collector may use a material selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, foam (foam) nickel, foam copper, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

The viscosity of the adhesive suspension may be 1-10000cps or 5-5000cps or 10-2000cps. When the adhesive suspension of the above viscosity is used, the adhesive suspension can be uniformly coated on the current collector, and the adhesive particles can be well spread toward the upper part in the drying process.

The electrode active material layer is formed by coating a binder suspension and coating an electrode slurry on the coated binder suspension. Alternatively, the electrode may be formed by simultaneous application of the binder suspension as a lower layer and the electrode slurry as an upper layer.

When the electrode is a positive electrode, the electrode active material may be used without limitation as long as it is a positive electrode active material generally used for a secondary battery. As an example, it may contain a material selected from LiCoO ₂ 、LiNiO ₂ 、LiMn ₂ O ₄ 、LiCoPO ₄ 、LiFePO ₄ 、LiNiMnCoO ₂ And LiNi _1-x-y-z Co _x M ¹ _y M ² _z O ₂ (M ¹ And M ² Is selected from Al, ni, co, fe, mn, V, cr, ti, W, ta, mg and Mo independently of each other, x, y and z are independently of each other the atomic fraction of the oxide constituent element, 0.ltoreq.x<0.5，0≤y<0.5，0≤z<0.5, x+y+z.ltoreq.1) or a mixture of two or more thereof.

When the electrode is a negative electrode, the electrode active material may be used without limitation as long as it is a negative electrode active material generally used for a secondary battery. As an example, the electrode active material may be a carbon-based anode active material, a silicon-based anode active material, or a mixture thereof, but is not limited thereto. The carbon-based negative electrode active material may be one or more selected from the group consisting of artificial graphite, natural graphite, and hard carbon. The silicon-based anode active material may be Si, siO _x (0<x<2) An Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), an Si-carbon composite, or at least one of them, and SiO ₂ Is a mixture of (a) and (b).

The electrode slurry may further comprise a conductive material, a binder, a thickener, or a combination thereof, as desired. The conductive material and the thickener may be the same as or different from those used in the adhesive suspension, and the present invention is not limited thereto.

The electrode paste may contain 90 wt% or more of the electrode active material, preferably 90 to 99.5 wt%, 95 to 99.5 wt% or 98 to 99.5 wt% of the electrode active material, and may contain 2.0 wt% or less or 1.5 wt% or less or 1.0 wt% or less of the binder, or may not contain the binder, with the balance being the conductive material and the thickener, with respect to the total amount of solids. Even if the content of the binder of the prepared electrode slurry is low, the interfacial adhesion of the current collector and the electrode active material layer can be improved due to the diffusion of the binder particles when the binder suspension is dried, and the rapid charging performance can be improved by reducing the resistance of the electrode surface.

An electrode for a secondary battery according to a specific embodiment of the present invention is characterized in that the following relation 1 is satisfied when the 90 ° bending adhesion of the electrode is measured.

In addition, the evaluation result of the 90 ° bending adhesive force of the electrode may be that at least 90 or more or 95 or more electrodes among 100 electrode samples manufactured satisfy the following relation 1.

[ relation 1]

t ₂ ≤t ₁ ≤8×t ₂

In the relation 1, the electrode active material may be one having the same particle size, t ₂ May be the particle size (D50) of the electrode active material.

In the above relation 1, the electrode active material may be obtained by mixing two or more electrode active materials having different particle diameters, t ₂ The particle size (D50) of one electrode active material contained in the highest weight among the mixed electrode active materials may be used.

In the above relation 1, the electrode active material may be obtained by mixing two or more electrode active materials having different particle diameters, t ₂ The particle size of the large particle size electrode active material (D50) in the mixed electrode active material may be. In this case, the large-particle-diameter electrode active material may be the electrode active material having the largest particle diameter among two or more electrode active materials having different particle diameters.

More specifically, in the relation 1, t may be ₂ ≤t ₁ ≤7×t ₂ 、t ₂ ≤t ₁ ≤6×t ₂ 、t ₂ ≤t ₁ ≤5×t ₂ 、t ₂ ≤t ₁ ≤4×t ₂ 、t ₂ ≤t ₁ ≤3×t ₂ Or t ₂ ≤t ₁ ≤2×t ₂ And may be 1.5×t ₂ ≤t ₁ ≤7×t ₂ 、1.5×t ₂ ≤t ₁ ≤6×t ₂ Or 1.5×t ₂ ≤t ₁ ≤5.5×t ₂ 。

Therefore, with the electrode of the present invention satisfying the above-described relation 1, when the 90 ° bending adhesive force of the electrode is measured, separation may occur inside the electrode active material layer, specifically, for example, when viewed in the electrode thickness direction, separation may occur from the current collector to a position corresponding to the thickness of the median particle diameter (D50) of the electrode active material particles or a position corresponding to 5 times the thickness of the median particle diameter (D50). That is, when the 90 ° bending adhesion of the electrode is measured, the position where separation occurs inside the electrode active material layer may be the electrode active material layer thickness t near the current collector side ₂ To 5 Xt ₂ Is a position of (c).

Specifically, it is understood that the electrode active material layer is a layer (1) in which active material particles are uniformly arranged in the width direction (in this case, the layer thickness is D50 of the electrode active material) and a plurality of such layers are laminated in the thickness direction. That is, in the present invention, the above-described results are analyzed according to the following: when the 90 ° adhesive force is measured, separation occurs at the position of 1 thickness (D50) of the active material particles in the thickness direction to 5 thicknesses (5×d50) of the particle unit.

Thus, the electrode of the present invention can improve the process failure and appearance failure such as interfacial detachment of the anode and can improve the quick charge performance even if the binder content in the anode slurry forming the anode active material layer is greatly reduced as compared with the conventional electrode.

The electrode can also satisfy the following relation 2, and thus the above effect can be further improved.

[ relation 2]

1.5×t ₂ ≤t ₁ ≤5×t ₂

More specifically, in the relation 2, it may be 1.5×t ₂ ≤t ₁ ≤4×t ₂ 、1.5×t ₂ ≤t ₁ ≤3×t ₂ Or 1.5×t ₂ ≤t ₁ ≤2×t ₂ 。

In addition, the electrode active material layer may be formed by applying a binder suspension to at least one side of the current collector and applying an electrode slurry on the applied binder suspension or simultaneously performing a step of applying a binder suspension to at least one side of the current collector and a step of applying an electrode slurry on the binder suspension and then drying the product thereof.

The particle size (D50) of the electrode active material in the present invention may be 1 to 20. Mu.m, 3 to 15. Mu.m, 7 to 15. Mu.m, or 9 to 15. Mu.m, but is not limited thereto. The particle size (D50) may refer to a particle diameter from a small particle diameter to a cumulative volume of 50% when the particle size distribution is measured by a laser scattering method. Wherein D50 can be sampled according to KS A ISO 13320-1 standard and the particle size distribution measured using a Mastersizer 3000 from Malvern. Specifically, the Volume density (Volume density) can be measured after dispersing using an ultrasonic disperser with ethanol as a solvent, if necessary.

The electrode may also satisfy the following relation 3.

[ relation 3]

0.25≤b ₂ /b ₁ <0.7

In the above relation 3, as for b ₂ /b ₁ In terms of the binder weight ratio, when a styrene-butadiene rubber (SBR) -based binder is used as the binder, os gas (gas) is adsorbed into the binder so that the content (atomic%) with respect to Os element can be applied, but this is not limited to Os element, and an element which can show a corresponding binder can be used depending on the kind of binder.

Specifically, b may be 0.25.ltoreq.b ₂ /b ₁ <B is 0.6 or 0.3 ₂ /b ₁ <0.6。

The electrode may also satisfy the following relation 4, in which case the above-described effect may be further improved.

[ relation 4]

0.3≤b ₂ /b ₁ <0.5

In the relation 4, b when the binder distribution is measured in the thickness direction of the electrode active material layer ₁ Is the weight of the binder in the whole electrode active material layer, b ₂ Is the weight of the binder in the region of 15% of the total thickness from the current collector to the electrode active material layer.

In the region of 15% of the total thickness from the current collector to the electrode active material layer, the binder may be contained in an amount of 0.2 to 7% by weight or 1 to 5% by weight or 1 to 4.5% by weight, relative to the total weight of solids of the region.

Further, the electrode active material layer is characterized in that the binder has a continuous concentration in the thickness direction of the electrode.

In the present specification, the binder "continuous" distribution may mean that the binder is uninterrupted and continuous in the electrode active material layer, rather than the binder suspension and the electrode slurry being formed as separate, distinct layers, and thus the value of the concentration (wt%) of the binder is continuous in the thickness direction of the electrode active material layer. The "concentration of the binder" may be the content (wt%) of the binder with respect to the total weight of the electrode active material layer per unit volume (cross-sectional area in the width direction×unit thickness) of the electrode active material layer.

More specifically, diffusion of the binder particles proceeds to a specific region from the interface with the current collector in the electrode active material layer to the active material layer, and thus the binder may be densely distributed while continuously present in the region. However, in the region of the electrode active material layer where diffusion of the binder particles does not proceed from the interface, there may be a trace amount of binder contained in the electrode slurry, and thus the binder may be distributed at a relatively high concentration in the region where the binder diffusion occurs. That is, the binder may exist in a specific region of the electrode active material layer in a continuous concentration due to diffusion of the binder particles in the binder suspension coated on the upper portion of the current collector.

Specifically, for example, when the interface of the current collector and the electrode active material layer is regarded as 0% of the thickness, as one example, the electrode active material layer is located on the current collector side, and may have a continuous binder concentration in the electrode thickness direction in a region of 0 to 35% or a region of 0 to 55% or a region of 0 to 75% or a region of 0 to 95% or a region of 0 to 100% (the entire electrode active material layer) of the total thickness of the electrode active material layer.

Therefore, the adhesive force (interfacial Adhesion) of the interface of the current collector and the electrode active material layer is stronger than the cohesive force (Cohesion) inside the negative electrode active material layer, and thus the interfacial adhesive force can be improved, and as the intercalation/deintercalation rate of lithium ions inside the electrode active material layer is improved, the rapid charging performance of the battery can be improved.

The electrode may also satisfy the following relation 5.

[ relation 5]

-30％≤(C-D)/D≤+30％

Specifically, it may be-25% or less (C-D)/D or-20% or less (C-D)/D or-15% or less (C-D)/D or-10% or less (C-D)/D or less than +10%. In the relational expression 5, C may be measured at a position having a certain interval in the width direction of the electrode active material layer, for example, at a position having an interval of 0.1 to 0.5mm or 0.2 to 0.3mm, and as an example, at a position having an interval of 0.25mm, but the present invention is not limited thereto.

According to one embodiment, the electrode may be a negative electrode.

Therefore, in the present invention, by using the binder suspension, in particular, by using a suspension containing a specific binder such as SBR, the high-content binder suspension can be uniformly coated in a relatively thin thickness and in the width direction of the current collector without forming a separate pattern, and the adhesion between the current collector and the electrode active material layer can be further improved as the binder particles diffuse to a specific region of the electrode active material layer.

In addition, the interfacial resistivity value between the electrode current collector and the electrode active material layer may be 0.1 Ω cm ² Below or 0.05 Ω cm ² Below or 0.03 Ω cm ² The following is given. According to the effects of the present invention described above, the interface resistivity value can be significantly reduced.

Another embodiment of the present invention provides a method of manufacturing an electrode for a secondary battery. The electrode manufacturing method includes the steps of: a) Coating an adhesive suspension on at least one side of a current collector; b) Coating an electrode slurry containing an electrode active material on an upper portion of the binder suspension; and c) drying the product of step b), wherein steps a) and b) are performed simultaneously or sequentially.

In step a), a current collector is prepared and an adhesive suspension is applied to at least one side of the current collector.

The types of binder and solvent and the current collector are as described above. The method for preparing the binder suspension may be a known method, and for example, the binder suspension may be prepared by mixing a specific binder such as the SBR-based binder in a solvent and diluting the mixture to have an appropriate viscosity, but the present invention is not limited thereto.

In said step a), the adhesive suspension may be uniformly coated on at least one side of the current collector. Uniformly coating the adhesive suspension in this specification means uniformly coating the adhesive suspension on the current collector such that the adhesive does not form a specific pattern.

According to one embodiment, in said step a), said adhesive suspension may be applied at a thickness of 0.1-10 μm. More specifically, the adhesive suspension may be coated to a thickness of 0.1-6 μm, 0.1-5 μm, 0.1-4 μm, 0.1-3 μm, 0.1-2 μm or 0.1-1 μm. At this time, the application thickness of the adhesive suspension means a value of the thickness measured in a state of being sufficiently dried after only the adhesive suspension is applied. When the thickness of the applied adhesive suspension is too thick, the adhesive suspension cannot be well mixed with the electrode paste, the distinction between their layers after drying is remarkable, and an adhesive layer as an insulator is formed, and thus interfacial resistance may be increased. On the other hand, when the coating thickness of the adhesive suspension is less than 0.1 μm, it may be difficult to achieve the desired object in the present invention. That is, in the above thickness range, it is possible to prevent an increase in interfacial resistance while improving interfacial adhesion between the current collector and the electrode active material layer, and to improve process defects such as electrode detachment.

According to one embodiment, the binder suspension contains 30 wt% or more of the binder with respect to the total amount of solids, and the electrode slurry may contain 2 wt% or less of the binder with respect to the total amount of solids. More specifically, the binder suspension may contain 30 wt% or more, 50 wt% or more, 70 wt% or more of the binder with respect to the total amount of solids, and the electrode slurry may contain 2 wt% or less, 1.5 wt% or less, 1 wt% or less of the binder with respect to the total amount of solids.

In step b) after step a), an electrode slurry containing an electrode active material is applied on top of the binder suspension.

The electrode active material is as described above, and any known method for forming an electrode paste for a known secondary battery may be used as a method for preparing the electrode paste.

As a non-limiting example of the application of the binder suspension of step a) and the application of the electrode slurry of step b), any known application method commonly used for applying a liquid phase to form a film may be used. For example, spray coating, dip coating, spin coating, gravure coating, slot die coating, knife coating (doctor blade coating), roll coating, ink jet printing, flexographic printing, screen printing, electrohydrodynamic printing, microcontact printing, embossing, reverse offset printing, bar coating, gravure printing (gravure offset printing), multilayer simultaneous die coating method, and the like can be used, but are not limited thereto.

Specifically, the binder suspension and the electrode paste may be sequentially coated, and the binder suspension and the electrode paste may be simultaneously coated by a multilayer simultaneous die coating method. However, in terms of uniformity or quality of the surface of the electrode, it is preferable to apply the electrode slurry after applying the binder suspension.

In step c) after step b), the product of step b) is dried.

In this case, the drying may be performed for 30 to 300 seconds, for example, 30 seconds or more, 40 seconds or more, 50 seconds or more, 60 seconds or more, 70 seconds or more, 80 seconds or more, or 90 seconds or more, and 300 seconds or less, 280 seconds or less, 260 seconds or less, 240 seconds or less, 220 seconds or less, 200 seconds or less, 180 seconds or less, 160 seconds or less, 150 seconds or less, 140 seconds or less, 130 seconds or less, 120 seconds or less, and 110 seconds or less. In addition, the drying may be performed at a temperature of 50 to 200 ℃, for example, at a temperature of 50 ℃ or more, 60 ℃ or more, 70 ℃ or more, 80 ℃ or more, or 90 ℃ or more, and 200 ℃ or less, 190 ℃ or less, 180 ℃ or less, 170 ℃ or less, 160 ℃ or less, 150 ℃ or less, 140 ℃ or less, 130 ℃ or less, 120 ℃ or less, or 110 ℃ or less. When the drying temperature is too high or the drying time is very short, the binder particles excessively diffuse, and thus interfacial adhesion may not be sufficiently achieved. As an embodiment, said step c) may be carried out at a temperature of 80-130 ℃ for 30-300 seconds.

Next, the dried electrode is pressed at an appropriate density, whereby an electrode having an electrode active material layer formed on a current collector can be manufactured. In this case, the pressing conditions and the pressing method such as the known pressing density may be applied, and the present invention is not limited thereto.

In the method for manufacturing an electrode for a secondary battery of the present invention, the binder particles of the binder suspension diffuse into the electrode active material layer and are present from the interface of the current collector and the electrode active material layer to a predetermined region of the electrode active material layer when the drying of step c) is performed, and thus, the problems of the decrease in interfacial resistivity value and adhesion between the current collector and the active material layer, which are problems occurring when the conventional binder solution is applied, can be improved.

Another embodiment of the present invention provides an electrode for a secondary battery, which is manufactured by a manufacturing method of an electrode for a secondary battery, the manufacturing method of the electrode for a secondary battery including the steps of: a) Coating an adhesive suspension on at least one side of a current collector; b) Coating an electrode slurry containing an electrode active material on an upper portion of the binder suspension; and c) drying the product of step b), wherein steps a) and b) are performed simultaneously or sequentially.

At this time, the electrode is as described above.

Also, the present invention provides a secondary battery including: the electrode; a diaphragm; and (3) an electrolyte.

The electrode is as described above.

The separator is not particularly limited as long as it is a separator known in the art. For example, the separator may be selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, may be in the form of a jersey or a woven fabric, and may optionally use a single-layer or multi-layer structure.

The electrolyte comprises a non-aqueous organic solvent and an electrolyte salt. The non-aqueous organic solvent may be Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), 1, 2-Dimethoxyethane (DME), γ -Butyrolactone (BL), tetrahydrofuran (THF), 1, 3-Dioxolane (DOL), diethyl ether (DEE), methyl Formate (MF), methyl Propionate (MP), sulfolane (S), dimethyl sulfoxide (DMSO), acetonitrile (AN), or a mixture thereof, but is not limited thereto. The electrolyte salt is a substance that is dissolved in a nonaqueous organic solvent and is used as a supply source of electrolytic metal ions in a battery so that the secondary battery can basically operate and promote movement of the electrolytic metal ions between a positive electrode and a negative electrode. As a non-limiting example, when the electrolytic metal is lithium, the electrolyte salt may be LiPF ₆ 、LiBF ₄ 、LiTFSI、LiSbF ₆ 、LiAsF ₆ 、LiClO ₄ 、LiCF ₃ SO ₃ 、Li(CF ₃ SO ₂ ) ₂ N、LiC ₄ F ₉ SO ₃ 、LiSbF ₆ 、LiAlO ₄ 、LiAlCl ₄ 、LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (wherein x, y are natural numbers), liCl, liI or mixtures thereof, but is not limited thereto. In addition, the electrolyte salt may use a known substance at a concentration that meets the object,and may further contain a known solvent or additive as needed to improve charge-discharge characteristics, flame retardant characteristics, and the like.

In the method of manufacturing a secondary battery of the present invention for achieving the object as described above, the manufactured negative electrode, separator, and positive electrode may be sequentially stacked to form an electrode assembly, and the manufactured electrode assembly may be placed in a cylindrical battery case or an angular battery case and then injected with an electrolyte to manufacture the battery. Alternatively, the electrode assembly may be impregnated with an electrolyte after being laminated, and the obtained product may be put into a battery case to be sealed to manufacture a battery.

The battery case used in the present invention may be a battery case commonly used in the art, and is not limited to the outer shape according to the use of the battery, and may be, for example, a cylindrical shape using a can, an angle shape, a soft pack (pouch) type, a coin (coin) type, or the like.

The secondary battery of the present invention may be used not only as a battery cell used as a power source of a small-sized device, but also preferably as a unit cell of a medium-sized and large-sized battery module including a plurality of battery cells. Preferable examples of the medium-to-large-sized devices include, but are not limited to, electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and systems for power storage.

Hereinafter, the present invention will be described in detail by way of examples, but these examples are only for explaining the present invention in more detail, and the scope of the claims of the present invention is not limited to the following examples.

Examples

Example 1

< production of negative electrode >

SBR (BM 451B of Zeon company) suspension was diluted in pure water as a binder to prepare a binder suspension.

Negative electrode active material, CMC thickener, SBR binder, which were mixed with artificial graphite (d50:13 μm) and natural graphite (d50:10 μm) in a weight ratio of 5:5, were added to water in a weight ratio of 98.5:1:0.5, thereby preparing a negative electrode slurry having a viscosity of 5000 cps.

The prepared binder suspension and negative electrode slurry were coated on one surface of a copper current collector (copper foil having a thickness of 8 μm) with a slit die by a multilayer simultaneous die coating method at a thickness of 1 μm (based on the thickness after drying when the binder suspension was coated alone) and 200 μm, respectively, and then dried, and then coated on the other surface in the same manner, and then dried. At this time, the drying conditions are described in the following table 5.

The dried negative electrode was pressed (pressed density: 1.68 g/cm) ³ ) Thereby manufacturing a negative electrode in which a negative electrode active material layer is formed on a current collector.

At this time, in the manufactured anode, the solid composition of the anode active material layer was 97.5 wt% of the anode active material, 1.5 wt% of the SBR binder, and 1 wt% of the CMC thickener. Further, the fabricated anode was formed of a copper foil having a thickness of 8 μm and an anode active material layer having a thickness of 127 μm, and it was confirmed on SEM images that the boundary of the binder layer and the anode active material layer was not clearly distinguished, but formed as one anode active material layer (refer to fig. 1).

< production of Positive electrode >

Li [ Ni ] as a positive electrode active material was mixed at a weight ratio of 96.5:2:1.5 _0.88 Co _0.1 Mn _0.02 ]O ₂ Carbon black as a conductive material and polyvinylidene fluoride (PVdF) as a binder to prepare a slurry. The slurry was uniformly coated on an aluminum foil having a thickness of 12 μm, and vacuum-dried to manufacture a positive electrode for a secondary battery.

< production of Secondary Battery >

The positive and negative electrodes were cut and laminated, respectively, in a predetermined size with a separator (polyethylene, thickness 13 μm) interposed therebetween to form an electrode battery, and then tab portions of the positive and negative electrodes were welded, respectively. The welded positive/separator/negative electrode assembly was placed in a soft pack and sealed on three sides except the electrolyte-filled side. At this time, the portion having the tab is included in the sealing portion.

Electrolyte is injected through the remaining surfaces except the sealing part, and the remaining surfaces are sealed and then immersed for 12 hours or more.

The electrolyte used was LiPF in which 1M was dissolved in a mixed solvent of EC/EMC/DEC (25/45/30; volume ratio) ₆ An electrolyte of 1 wt% Vinylene Carbonate (VC), 0.5 wt% 1, 3-propane sultone (PRS) and 0.5 wt% lithium bis (oxalato) borate (LiBOB) was then added.

Thereafter, the cell was precharged (Pre-charging) for 36 minutes at a current corresponding to 0.25C. Degassing (Degasing) was performed after 1 hour, aging was performed for 24 hours or more, and then formation charge and discharge (charging condition: CC-CV 0.2C4.2V 0.05C CUT-OFF (CUT-OFF)) was performed, and discharging condition: CC 0.2C2.5V CUT-OFF (CUT-OFF)).

Thereafter, standard charge and discharge (charge condition: CC-CV 0.33C 4.2V 0.05C CUT-OFF (CUT-OFF) and discharge condition: CC 0.33C 2.5V CUT-OFF (CUT-OFF)) were performed.

Example 2

A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that the binder suspension was coated by gravure coating and then the negative electrode slurry was coated by a slot die in the process of coating the binder suspension and the negative electrode slurry.

Example 3

Negative electrode, positive electrode and secondary battery were manufactured by the same method as in example 1, except that SBR (BM 451B of Zeon company) and CMC (D2200 of Daicel company) were used as binders and were mixed and diluted in a solid matter ratio of 97:3, respectively, to prepare a binder suspension.

Example 4

A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that the prepared binder suspension and negative electrode slurry were coated on one surface of a copper current collector (copper foil having a thickness of 8 μm) by a multilayer simultaneous die coating method using a slit die at a thickness of 7 μm (based on the thickness after drying when the binder suspension was coated alone) and 132 μm, respectively.

Comparative example 1

The negative electrode active material, SBR binder and CMC thickener, which were mixed with artificial graphite (D50: 13 μm) and natural graphite (D50: 10 μm) in a weight ratio of 5:5, were added to water in a weight ratio of 97.5:1.5:1, thereby preparing a negative electrode slurry having a viscosity of 5000 cps.

The prepared negative electrode slurry was coated on one surface of a copper current collector (copper foil having a thickness of 8 μm) by a die coating method using a slit die, then dried, and similarly coated on the other surface, then dried. The dried negative electrode was pressed (pressed density: 1.68 g/cm) ³ ) Thereby manufacturing a negative electrode in which a negative electrode active material layer is formed on a current collector.

At this time, the negative electrode was formed of a copper foil having a thickness of 8 μm and a negative electrode active material layer having a thickness of 126 μm.

A positive electrode and a secondary battery were manufactured by the same method as in example 1, except that the manufactured negative electrode was used.

Comparative example 2

The negative electrode active material, SBR binder, CMC thickener, which were mixed with artificial graphite and natural graphite in a weight ratio of 5:5, were added to water in a weight ratio of 97:2:1, thereby preparing a first negative electrode slurry.

The negative electrode active material, SBR binder, CMC thickener, which were mixed with artificial graphite and natural graphite in a weight ratio of 5:5, were added to water in a weight ratio of 98:1:1, thereby preparing a second negative electrode slurry.

The prepared first negative electrode slurry and second negative electrode slurry were coated on one side of a copper current collector (copper foil having a thickness of 8 μm) by a multilayer simultaneous die coating method using a slit die so that a thickness of 5:5 could be formed, and then dried and pressed (pressed density: 1.68 g/cm) ³ ) Thereby manufacturing a negative electrode in which the first negative electrode active material layer and the second negative electrode active material layer are formed on the current collector. A positive electrode and a secondary battery were manufactured by the same method as in example 1, except that the manufactured negative electrode was used.

Comparative example 3

Negative electrodes, positive electrodes and secondary batteries were manufactured by the same method as in example 1, except that a binder suspension was prepared using CMC (D2200 of Daicel corporation) as a binder.

Comparative example 4

A negative electrode, a positive electrode, and a secondary battery were produced by the same method as in example 1, except that PAA (SW 100 of sumitomo refinement) was used as a binder to prepare a binder suspension.

Comparative example 5

A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that CMC (D2200 of Daicel corporation) and PAA (SW 100 of sumitomo refinement corporation) were used as binders and mixed and diluted in a solid matter ratio of 1:3 to prepare a binder solution.

Comparative example 6

The prepared binder suspension was coated on one side of a copper current collector by a slot-die coating method, and then dried to form a binder layer, and a negative electrode slurry was coated on the formed binder layer by a slot-die coating method, and then dried to form a negative electrode active material layer. Thereafter, except for pressing (pressed density: 1.68g/cm ³ ) A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that a negative electrode in which a binder layer and a negative electrode active material layer were formed on a current collector was manufactured.

Evaluation example 1]By X-ray Energy Dispersive Spectroscopy (EDS) Evaluation of Binder distribution Properties in the negative electrode thickness direction and Binder distribution Properties in the negative electrode surface direction of the map

SEM image (image) results of the cross-sections in the thickness direction of the electrodes manufactured in example 1 and comparative example 6 are shown in fig. 1 and 2, respectively, and EDS mapping results in the thickness direction of the electrodes manufactured in example 1 are shown in fig. 3 and 4. At this time, it is difficult to distinguish the distribution of SBR binder by ordinary EDS mapping, so Os gas is sufficiently exposed to the electrode, and then an image of EDS mapping analysis of Os element is shown in fig. 3, and the distribution (profile) of mass% of SBR (Os) content in the electrode thickness direction is shown in fig. 4.

Referring to fig. 1, it can be seen that the distinction between the binder layer and the active material layer of the electrode manufactured in example 1 is unclear, and analysis is because the SBR binder diffuses into the electrode active material layer. By using the SBR binder suspension, the binder suspension can be coated at a sufficiently thin thickness, and it can be confirmed by SEM images that the contact of the current collector and the active material layer is formed very closely as the SBR binder particles diffuse to the electrode slurry layer during the drying of the electrode, as if the binder layer was not further coated. On the other hand, in fig. 2, a separate adhesive layer different from the electrode active material layer was formed by applying and drying the adhesive, and it was also confirmed in the SEM image that the adhesive layer and the active material layer were formed on the current collector, respectively.

Therefore, it was confirmed that an electrode having no increase in interfacial resistivity value could be produced without applying conventional die Coating (pattern Coating) and uniformly Coating an adhesive layer as an insulator in the width direction.

Referring to fig. 3 and 4, it can be confirmed that the binder is continuously distributed at a relatively high concentration in a partial region from the boundary of the electrode current collector and the active material layer to the active material layer. From this result, it is understood that not only the adhesive force of the boundary of the current collector and the electrode active material layer can be greatly improved, but also the adhesive force of the predetermined region of the lower portion of the electrode active material layer can be improved because the adhesive particles are diffused to the electrode active material layer during the drying process.

Further, the results of analysis of SEM images and EDS maps of the thickness direction cross sections of the electrodes of examples 1 to 4 and comparative examples 1 to 6 are shown in table 1 below. Specifically, the content a of Os element per unit thickness was measured for the entire region of the active material layer ₁ (atomic%) and utilize the a ₁ Content b of Os element converted to whole region ₁ . Measuring the content a of Os element per unit thickness for a region from the current collector to a thickness corresponding to 15% ₂ (atomic%) and utilize the a ₂ Content b of whole Os in terms of 15% thickness ₂ . Next, calculate b ₂ /b ₁ And is shown in table 1 below.

TABLE 1

It was confirmed that a large amount of binder was distributed at the interface between the current collector and the active material layer in examples 1 to 3, but it was found that comparative example 1 was insufficient in binder distributed at the interface between the current collector and the active material layer compared to the average binder content of the entire active material layer due to the binder diffusion phenomenon. The content of the binder distributed at the interface of comparative example 2 was increased as compared with comparative example 1, but showed a low value as compared with example. This means that in the case of examples 1 to 3, the current collector and the active material layer are relatively more firmly bonded together, and rapid charging performance is facilitated due to the low binder content of the active material layer surface.

Evaluation example 2]Evaluation of interlayer adhesion and interfacial resistivity values of electrodes

1) Measurement of 90 ° bending adhesion of electrodes

The 90 ° bending adhesion was measured for the electrodes manufactured in examples 1 to 4 and comparative examples 1 to 6, and the measured adhesion and the position separated from the electrodes are described in table 2 below. Fig. 5 (a) to 5 (d) are schematic diagrams each showing a state in which the current collector and the electrode active material layer are separated.

* Evaluation of interfacial adhesion of electrode active material layer and current collector

The negative electrodes manufactured in examples 1 to 4 and comparative examples 1 to 6 were cut into 18mm in the transverse direction/150 mm in the longitudinal direction, and a single-sided tape (tape) (manufactured by 3M company) having a width of 18mm was adhered at a position of 100mm other than about 50mm in the longitudinal direction serving as a fastening portion to a tensile tester in one side of the electrode coated on both sides, and then sufficiently adhered with a roller (roller) having a load of 2 kg. The double-sided tape was stuck to the bottom surface of the tensile tester, and then the double-sided tape surface and the single-sided tape surface of the above electrode manufactured were stuck to face each other. The portion to which the single-sided tape was not attached was fastened at the other side of the tensile tester, the 90 ° bending adhesive force (fig. 6a and 6 b) was measured, and the result of dividing the measured strength by the width of the tape is summarized in table 2 below. Further, the adhesion force of the negative electrodes of example 1 and comparative example 1 was measured, and then the separated negative electrode photograph was shown in fig. 6 c.

In addition, i) the average separation position t ₁ Is a value obtained by measuring the 90 ° bending adhesion using electrodes coated on both sides and measuring the thickness of the portion containing the current collector in the separated two portions, and then subtracting the thicknesses of the current collector and the following active material layer. The thickness of the electrode was measured using a micrometer (series 293, mitsutoyo) having a tip (tip) of 6.35pi, and a measurement pressure of 5N, and an average value of 8 times after 10 times of measurement was taken as the thickness of the electrode.

ii) particle size t of the active substance ₂ The particle size (D50) of the graphite active material used in examples and comparative examples was the particle size (D50) of the large-particle-diameter graphite active material having a large particle diameter. At this time, the particle size of the large particle size graphite active material was 13. Mu.m.

TABLE 2

Fig. 5 (a) is a schematic view showing the result of measuring 90 ° bending adhesion force for the electrodes manufactured in examples 1 to 3. Referring to table 2 and (a) of fig. 5, it is apparent that the cohesive force inside the electrode active material layer is weak compared to the adhesive force of the interface between the current collector and the electrode active material layer, and thus separation occurs inside the negative electrode active material layer. That is, when the binder content in the electrode active material layer is low, the form of fig. 5 (a) is obtained, and from this result, it is clear that the binder content in the electrode active material layer is low in the binder distribution. A photograph of the separated negative electrode after the measurement of the adhesive force of example 1 can be confirmed in fig. 6 c.

Fig. 5 (b) is an electrode manufactured in comparative examples 1 to 2, and is a schematic view showing a state in which the current collector and the electrode active material layer are separated when 90 ° bending adhesion force is measured for a general electrode in which the electrode slurry is directly coated and dried on the upper portion of the current collector to form the active material layer. Referring to table 2 and (b) of fig. 5, it was confirmed that in the above case, the adhesive force of the current collector and the electrode active material layer was lower than the cohesive force inside the electrode active material layer, and thus separation occurred at the interface.

Fig. 5 (c) is an electrode manufactured in comparative examples 3 to 6, and is a schematic view showing a form in which 90 ° bending adhesive force is measured for the case of coating an electrode active material layer on a current collector dried after previously coating an adhesive layer (comparative example 6) or the case of manufacturing an adhesive that can realize an adhesive suspension when CMC and/or PAA are used instead of SBR or the like is mixed with a solvent (comparative examples 3 to 5). In this case, separation occurs at the interface between the binder layer and the electrode active material layer, and referring to table 2 and (c) of fig. 5, it is known that in the case of using CMC and PAA binder instead of SBR and in the case of applying the anode active material layer after drying the SBR binder suspension, the binder does not sufficiently diffuse to the electrode active material layer. Therefore, it was confirmed that the binder layer and the electrode active material layer were clearly formed as respective layers, and that the adhesive force of the interface of the formed binder layer and the anode active material layer was the weakest, and thus separation occurred at this position.

In addition, (d) of fig. 5 is a negative electrode manufactured in example 4, which is similar to (a) of fig. 5, but (d) of fig. 5 shows a case where the boundary of the binder layer and the active material layer is clearly distinguished. Referring to table 2 and (d) of fig. 5, when a thick SBR adhesive suspension having a standard value or more is applied, the interfacial adhesion is improved by the diffusion of SBR particles, but a thick adhesive layer may be formed to function as an insulating layer.

In addition, referring to Table 2, it was confirmed that the electrode according to the present invention was formed as a "layer" of the active material when measuring the adhesive forceThe form of "remains separated in the state of the current collector, so the electrode always has 1.0×t ₂ The above thickness. Further, the photograph of example 1 of fig. 6c was visually checked, and it was found that the upper and lower layers were both active material layers. The average separation position satisfies relation 1 of the present invention.

On the other hand, the existing electrode to which the technique of the present invention is not applied was separated from the current collector at the interface, but it was confirmed that the active material particles were not cleanly separated from the boundary but unevenly separated in particle units. Specifically, the photograph of comparative example 1 of fig. 6c was visually confirmed that most of the active material particles were Cu current collector, and a small amount of active material particles remained as if scattered in a partial region, unlike the case of example 1 in the form of "active material layer". At this time, the average separation position thickness is 0.ltoreq.t ₁ <1.0×t ₂ The relation 1 of the present invention is not satisfied. The result was analyzed because the tip size (size) of the thickness gauge was as wide as 6.35pi, thus containing a large amount of active material particles and being measured as an average thickness.

2) Measurement of interfacial resistivity values of electrodes

For the electrodes manufactured in examples 1 to 4 and comparative examples 1 to 6, interfacial resistance between the electrodes and the current collectors was measured using a Hioki interfacial resistivity value meter (Hioki XF 057), and the results thereof are shown in table 3 below.

TABLE 3

	Interfacial resistivity value (ohm cm) ² )
		Example 1	0.007
Example 2	0.006
		Example 3	0.008
Comparative example 1	0.011
		Comparative example 2	0.012
Comparative example 3	Cannot be measured
		Comparative example 4	Cannot be measured
Comparative example 5	Cannot be measured
		Comparative example 6	0.083
Example 4	0.257

Referring to table 3, the electrodes manufactured in examples 1 to 3 of the present invention also had the interface resistivity values between the electrode and the current collector measured at the same level as those of comparative examples 1 to 2 in the case of coating the binder suspension. On the other hand, in comparative examples 3 to 5, sufficient adhesion was not ensured, and thus reliable interfacial resistivity values could not be measured after pressing. Comparative example 6 shows that, since the binder suspension is not mixed with the electrode active material, a clearly differentiated binder insulator layer is formed between these layers after drying. It was found that the thick insulator adhesive layer was formed in analytical example 4 and thus showed the highest interfacial resistance.

Evaluation example 3]Evaluation of quick Charge Performance

The secondary batteries manufactured in examples 1 to 4 and comparative examples 1 to 6 were subjected to a fast charge evaluation of charging at a rate of 2.5C (C-rate) and discharging at a rate of 1/3C at a temperature of 25 ℃. The quick charge capacity retention was measured after repeating 100 cycles and 200 cycles, and the results thereof are shown in table 4 below.

TABLE 4

Referring to table 4, it was confirmed that the cycle capacity retention (%) of the secondary batteries manufactured in examples 1 to 3 was reduced less than that of comparative examples 1 to 3, and excellent quick charge performance was ensured. As analyzed, the binders of comparative examples 1 to 2 were uniformly dispersed on the electrode surface, so that the electrode resistance increased, and the rapid charge characteristics were deteriorated, and comparative examples 3 to 5 failed in battery fabrication due to the occurrence of defects in which the electrode active material layer was detached from the current collector portion during the pressing (Press) and cutting processes. As shown in table 3, the specific resistance value of the interface between the current collector and the active material layer in comparative example 6 and example 4 was increased, and thus the capacity characteristics were deteriorated as charge and discharge cycles were performed.

Evaluation example 4]Evaluation of adhesion between active Material layer and Current collector according to electrode drying Condition

(examples 5 to 9)

An electrode was manufactured by the same method as in example 1, except that the drying process of the coated electrode paste in step 2 of example 1 was performed as described in table 5 below.

Comparative example 7

An electrode was manufactured by the same method as in comparative example 3, except that the drying process of comparative example 3 was performed as described in table 5 below.

(evaluation method)

The interfacial adhesion between the active material layer and the current collector was evaluated in the same manner as in evaluation example 2, and the results are shown in table 5 below.

TABLE 5

Referring to table 5, it was confirmed that in the case where the drying temperature was as low as 120 ℃ or less (example 1, example 5, example 6 and example 9), the drying time was increased in order to evaporate all the solvents, but the binder particles of the binder suspension diffused to the electrode active material layer, and thus the adhesion between the current collector and the active material layer was increased. It was analyzed that when the drying temperature was too high (example 7, example 8), the active material particles were easily exposed to the solvent surface during the drying due to the rapid drying, and thus the adhesive force was slightly lowered due to excessive diffusion of the adhesive particles due to the capillary phenomenon.

In the case of comparative example 7, it was confirmed that even if the same drying process as in example 6, which is the most excellent condition for adhesion, was performed, the lowest adhesion was exhibited.

Evaluation example 5]Binder distribution characteristics in the width direction of the electrode active material layer interface

The negative electrode manufactured in example 1 was cut to have a width direction of 18 mm/350 mm in the longitudinal direction, and a single-sided tape (manufactured by 3M company) having a width of 18mm was adhered to a position of 300mm other than about 50mm in the longitudinal direction serving as a fastening portion to a tensile tester in one side of the electrode coated on both sides, and then sufficiently adhered with a roll having a load of 2 kg. The double-sided tape was stuck to the bottom surface of the tensile tester, and then the double-sided tape surface and the single-sided tape surface of the above electrode manufactured were stuck to face each other. A portion to which a single-sided tape was not attached was fastened at the other side of the tensile tester, 90 ° bending adhesive force was measured for a total of 1201 areas having a spacing of 0.25mm in the width direction of the negative electrode, and the measured strength was divided by the width of the tape, and the result is shown in fig. 7. Next, the dispersion (%) characteristics of the adhesive strength measured in the 1201 areas are shown in fig. 8. At this time, the spread (%) is calculated as (individual value of adhesion in each region-adhesion average value)/adhesion average value).

Referring to fig. 7 and 8, it was confirmed that the active material layer of the electrode manufactured in example 1 was formed by uniformly distributing SBR binder particles in the width direction.

Evaluation example 6]Evaluation of electrode interlayer bonding force according to active Material particle size

Example 10

The binder suspension was prepared by diluting SBR (BM 451B of Zeon company) suspension as a binder in pure water.

SiO was added in a weight ratio of 98:1:1.0 _x The base anode active material (D50: 6 μm), CMC thickener, and SBR binder were added to water, thereby preparing an anode slurry having a viscosity of 5000 cps.

A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that the prepared binder suspension was coated on one surface of a copper current collector (copper foil having a thickness of 8 μm) by gravure coating and then a negative electrode slurry was coated using a slot die. At this time, the thickness of the adhesive suspension applied by gravure coating was 2 μm (based on the thickness after drying when the adhesive suspension was applied alone), and the thickness of the finally applied electrode was 204 μm.

The dried negative electrode was pressed (pressed density: 1.68 g/cm) ³ ) To manufacture a negative electrode in which a negative electrode active material layer is formed on a current collector.

Example 11

SBR (Zeon BM 451B) suspension was diluted in pure water as a binder to prepare a binder suspension.

SiC-based negative electrode active material (D50: 2 μm), CMC thickener, SBR binder were added to water at a weight ratio of 98:1:1.0, thereby preparing a negative electrode slurry having a viscosity of 5000 cps.

A negative electrode, a positive electrode, and a secondary battery were manufactured by the same method as in example 1, except that the prepared binder suspension was coated on one surface of a copper current collector (copper foil having a thickness of 8 μm) by gravure coating and then a negative electrode slurry was coated using a slot die. At this time, the thickness of the adhesive suspension applied by gravure coating was 2 μm (based on the thickness after drying when the adhesive suspension was applied alone), and the thickness of the finally applied electrode was 200 μm.

The interfacial adhesion between the electrode active material layer and the current collector was evaluated in the same manner as in evaluation example 2. The measured 90 ° bending adhesion and the position of separation in the electrode are shown in table 6 below.

TABLE 6

(in said Table 6, t ₂ The particle size of the large-particle-diameter anode active material in the mixed anode active material (D50). )

Referring to Table 6, it was confirmed that the electrode according to the present invention was separated in a state that the active material remained in the form of a "layer" in the current collector when the adhesive force was measured, and thus the electrode always had a thickness of 1.0×t ₂ The above thickness. Further, compared with examples 10 to 11, it was confirmed that the average separation position was in a preferable rangeExample 1 in the above shows more excellent adhesion.

The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments, but may be manufactured in various different ways, and those skilled in the art will appreciate that the present invention may be implemented in other specific ways without changing the technical ideas or essential technical features of the present invention. Accordingly, it should be understood that the above-described embodiments are illustrative in all respects and not restrictive.

Claims

1. An electrode for a secondary battery, comprising:

a current collector; and

an electrode active material layer on at least one side of the current collector,

and satisfies the following relation 3,

[ relation 3]

0.25≤b ₂ /b ₁ <0.7

2. The electrode for a secondary battery according to claim 1, wherein the electrode further satisfies the following relational expression 2,

[ relation 2]

1.5×t ₂ ≤t ₁ ≤5×t ₂

In the relation 2, t ₁ Is the thickness of the electrode active material layer, t, on the side of the current collector, excluding the current collector, based on the position where separation occurs inside the electrode active material layer when measuring the 90 DEG bending adhesion of the electrode ₂ Is the particle size D50 of the electrode active material contained in the electrode active material layer.

3. The electrode for a secondary battery according to claim 1, wherein the electrode active material layer comprises a styrene-butadiene rubber-based binder.

4. The electrode for a secondary battery according to claim 3, wherein the electrode active material layer contains 0.1 to 2 wt% of the binder with respect to the total weight.

5. The electrode for a secondary battery according to claim 1, wherein the electrode further satisfies the following relational expression 4,

[ relation 4]

0.3≤b ₂ /b ₁ <0.5

6. The electrode for a secondary battery according to claim 1, wherein the electrode has a continuous binder concentration in a thickness direction of the electrode.

7. The electrode for a secondary battery according to claim 1, wherein the electrode further satisfies the following relational expression 5,

[ relation 5]

-30％≤(C-D)/D≤+30％

8. The electrode for a secondary battery according to claim 1, wherein the electrode is a negative electrode.